Method of casting aluminum cylinder

ABSTRACT

A method and an apparatus are provided for forming an article of manufacture comprising a die-cast hollow piece. A core member, consisting of substantially the same composition as that comprising the hollow piece, is at least partially coated with an anti-adhering layer. The core member is located within a mold having a cavity for receiving the molten die casting material and for forming the outer surface of the hollow piece. The molten material is introduced into the cavity and cooled until solidification, at which time, the mold is removed from around the hollow piece. A major portion of the core member is machined out from the cast piece and the coated portions of the core remaining within the piece are knocked out from therein by mechanical impaction.

United States Patent 1 Frederickson 1 1 Nov. 12, 1974 l l METHOD OFCASTING ALUMINUM 22 Filed: Mar. 17, 1970 1211 Appl. No.: 20,202

[52] U.S. Cl. 164/132, 164/345 [51] Int. Cl 822d 29/00 [58] Field ofSearch 164/72, 75, 131, 132, 267,

3,401,735 9/1968 Pursall 164/1311 X Primary Examiner-Andrew R. JuhaszAssistant Examiner-John S. Brown Attorney, Agent, or FirmBurns, Doane.Swcckcr & Mathis [57] ABSTRACT A method and an apparatus are providedfor forming an article of manufacture comprising a die-cast hollowpiece. A core member. consisting of substantially the same compositionthat comprising the hollow piece. is at least partially coated with ananti-adhering layer. The core member is located within a mold having acavity for receiving the molten die casting material and for forming theouter surface of the hollow piece. The molten material is introducedinto the cavity and cooled until solidification. at which time, the moldis removed from around the hollow piece. A major portion of the coremember is machined out from the cast piece and the coated portions ofthe core remaining within the piece are knocked out from therein by mechanical impaction.

14 Claims, 9 Drawing Figures PATENTEDHUV 12 1974 SHEEI 10F 2 INVENTORROBERT EUGENE FREDERICKSON 1 METHOD OF CASTING ALUMINUM CYLINDERBACKGROUND OF THE INVENTION This invention relates to the casting ofhollow pieces by the use of what are usually characterized as permanentmolds and which are hereinafter referred to merely as molds". Morespecifically, the invention is directed to an improved method andapparatus for die casting articles of manufacture having irregularhollow cavities and holes formed therein.

Manufacturers are currently faced with the problem of providingmachinery, such as pumps and internal combustion engines, having higherrequirements than have heretofore been called for with respect to cost,weight and tolerance criticality.

Pump bodies and internal combustion engine blocks are presently beingmanufactured by various die casting processes. A common method forcasting lightweight internal combustion engine cylinders is to cast analuminum body around an iron liner having various ports and blistersformed therein. Upon cooling, the aluminum cylinder having the ironliner cast therein, is machined to provide inlet and exhaust ports whichextend entirely through the walls of the cylinder. This machining may beextensive and must be precise so as to constitute a time-consuming andexpensive step in the cylinder forming process.

The iron liner about which the cylinder body is cast often has differentheat expansion and heat transfer characteristics than the surroundingaluminum. As the result of these property differences, the iron linerand the surrounding body do not expand evenly when operationallyincorporated in an internal combustion engine application. This unevenexpansion causes distortion of the cylinder at elevated temperatureswhich distortion, in turn, causes a loss of engine power. Sincedistortion upsets the critical tolerances of an engine, the seal betweenpiston rings and the inner bore surface of the cylinder becomes lesseffective and blow-by may result which has the effect of corrodingvarious elements ofthe engine such as the wrist pins. Additionally, thedifferent heat transfer coefficient of the iron liner with respect tothe surrounding aluminum cylinder body presents cooling problems inconducting heat from within the cylinder, through the iron liner,through the aluminum body and, thence, to the cooling fins formed on thecylinder. Also, the existing need for lightweight engines militatesagainst the use of a heavy iron liner so that it would be an overallimprovement in the art if many lightweight cylinder configurations couldbe easily formed without including such a liner.

The present invention is therefore directed to the die casting ofarticles such as aluminum internal combustion engine cylinders whichheretofore have been traditionally constructed as composite articles.

In die casting hollow articles having high tolerance requirements, itwas found that different heat expansion and heat transfercharacteristics of core members with respect to the material being castresulted in distorted and imperfect tolerances when the cores were usedto form internal surfaces such as the bore of an l.C.E. (internalcombustion engine) cylinder. Because of this, efforts were made totraverse the teachings of the prior art by discovering a way to form acylinder of unitary construction by using a core member consisting ofthe same material as that comprising the die casting material.

Initially, it was discovered that using an aluminum core to form thebore within an aluminum l.C.E. cylinder often resulted in fusion betweenthe cast article and the core which fusion made it necessary toextensively machine the overall core and cast article upon the removalthereof from the molds. This result was especially noticeable when acore was used which had protuberances for forming inlet, outlet andtransfer ports within the cylinder.

It was then decided that an attempt should be made to identify a coatingwhich could be applied to the arti- -cle forming surface of the core andwhich might operate as an anti-adhering film to prevent fusion, brazingor welding of the core to the cast article. Upon anodizing the aluminumcore with a refractory substance, it was discovered that fusion oftenresulted between the core and the cast article. Currently, manufacturersare anodizing cores in order to control the heat conductivity of themold and not to prevent fusion of the core with the cast article.

A similar result of fusion between the core and cast article occurredwhen the core member was coated with a high temperature porcelainsubstance.

After these earlier unsatisfactory results it was unexpectedly foundthat anti-adhering substances which are resistant to temperatures andpressures in excess of those encountered in die casting processes maysuccessfully prevent fusion between the core and article and mayfacilitate the removal of the core from the article after cooling. Thesesubstances should be substantially impermeable and should volatize onlyat very high temperatures. It was ultimately discovered that hightemperature tetrafluoroethylene, hard chrome, and various solutions ofpolyimide, when brushed, plated, or sprayed onto an aluminum core andthen baked thereon will prevent fusion between the core and a castarticle.

OBJECTS AND SUMMARY OF THE INVENTION It is therefore an object of thepresent invention to provide a novel means and method for die castinghollow articles.

It is another object of the present invention to provide a novel meansand method for preventing the fusion of portions of a core member with acast article when the two consist of substantially identical material.

It is still another advantage of the present invention to provide amethod and apparatus for die casting metallic internal combustion enginecylinders which will have less distortion at elevated temperatures andwhich will allow closer tolerances so as to produce increased enginepower.

It is yet another object of the present invention to provide novelmethod and means for die casting internal combustion engine cylinders ofa new, lightweight, unitary construction which satisfies close tolerancerequirements.

It is a further object of the present invention to provide an internalcombustion engine cylinder having improved cooling characteristics.

lt is still a further object of the present invention to provide aninternal combustion engine cylinder which is uncomplicated andinexpensive to manufacture.

The objects of the present invention are carried out by providing amethod and an apparatus for casting hollow articles in which molten diecasting material is introduced into a die having a core positionedtherein. The die casting material is cooled until it solidifies and isthen removed from the mold. A major portion of the core is machined fromwithin the cast article which is then mechanically impacted to knock-outthe remaining portions of the core.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is particularly pointedout and distinctly claimed in the concluding portion of thespecification and several embodiments are disclosed herein which maybest be understood when taken in connection with the accompanyingdrawings, in which:

FIG. 1 is a sectional view taken along the axis of an internalcombustion engine cylinder constructed in accordance with the method andapparatus of the present invention;

FIG. 2 is a sectional view of the internal combustion engine cylinder ofFIG. 1 taken along line 22 of FIG.

FIG. 3 is a pictorial view of a core member used to form the bore andvarious ports within the cast internal combustion engine cylinder shownin FIG. 1;

FIG. 4 is a pictorial view of the core member shown in FIG. 3 properlylocated within a mold for casting an internal combustion enginecylinder;

FIG. 5 is a schematic view showing blister forming protuberances on acore member which protuberances are formed with bosses extendingradially through a cast cylinder wall into a wall of the die;

FIG. 6 shows the blister forming protuberances of FIG. 5 after thebosses have been mechanically impacted so as to knock the protuberancesfrom within the cylindrical wall of the cast article;

FIG. 7 is a partial sectional view of a protuberance having a boss whichis tapered to narrow toward the outer end thereof;

FIG. 8 is a partial sectional view of a protuberance being knocked outby a punch inserted within a hole formed in the cylinder wall; and

FIG. 9 is a partialsectional view of the portion of a cylinder shown inFIG. 8 after the protuberance has been knocked out and the hole properlysealed.

DETAILED DESCRIPTION Referring now to the drawings, in which likenumerals are used to indicate like parts throughout the various viewsthereof:

FIG. I shows a sectional view of an internal combustion engine cylinder10 having an internal bore 12. A charge inlet port 14 is formed withinthe wall of the cylinder 10 near the lower portion thereof. An exhaustport 16 is formed within the wall of the cylinder 10 above the inletport 14 so as to facilitate scavenging when the cylinder is used inconnection with a two stroke internal combustion engine. By-pass ortransfer ports 18 are formed as blisters within the wall of the cylinder10. The ports 18 are positioned vertically between the inlet port 14 andexhaust port 16 and are spaced angularly therefrom. Each blister I8 mayvary in configuration in accordance with the by-pass re quirements ofthe specific engine design. Referring briefly to FIG. 2, it can be seenthat the general extension of the blisters 18 along line e does notcoincide with a radial r drawn to the approximate center of the blister.This offsetting angle, which may be approximately 30, is significant inthat such angles are difficult to machine using current methods ofmanufacture.

Returning to FIG. 1, a generally cylindrical recess 20 is formed in thehead of the cylinder 10 which recess may be used to retain a spark plug(not shown). The generally spherical portion 22 defining the upperportion of the bore 12 may be used as the combustion chamber of thecylinder and may be of an irregular configuration. Cooling fins 24 areformed on the outer cylindrical surface of the cylinder 10 for effectingheat transfer from the combustion area 22 to the atmosphere surroundingthe cylinder 10.

Referring now to FIG. 3, a core member 30 is shown which may be used toform the bore 12, the blisters I8, and the ports 14 and 16 of theinternal combustion engine cylinder 10 shown in FIG. 1. The core member30 may consist of the same material as the engine cylinder 10 and may beformed with an inner cylindrical surface 32 which defines a recess forreceiving a core arbor or positioner 50 of a die described hereinafterin refer ence to FIG. 4. A radially projecting protuberance 38 isprovided on the cylindrical surface of the core member 30 to form theexhaust port 16 shown in FIG. I and a second protuberance 40 forms theinlet port 14 shown in the same view. An irregular protuberance 42 isformed on the core member 30 vertically between the radial projections38 and 40 but is angularly spaced therefrom to form the irregularblisters 18 shown in FIGS. 1 and 2. It will be noted that surface 44 ofthe projection 42 subtends an angle of approximately 30 with respect toa plane extending tangent to the cylindrical surface of the core 30 at aline common to the outer surface of the cylindrical core 30 and thesurface 44 of the projection 42. The significance of this irregularconfiguration has been previously discussed with respect to FIGS. 1 and2.

The core member 30 shown in FIG. 3 may be die cast of a lightweightmetal such as aluminum or magnesium by any conventional means. If it isdesired to die cast a hollow article such as a pump body of anonmetallic substance or of any die castable material, it is preferable,although not necessary, that the core member 30 comprise the samematerial as the die casting material to practice the present invention.

Upon casting the core 30 of the same material as that comprising thehollow cast article, a heat and pressure resistant anti-adheringsubstance is coated at least on the protuberance surfaces of the coremember 30 by a dipping, plating, brushing, or spraying operation.

The coating may comprise a substance such as a liquidized polyimidecomposition or a silicone oil. A coating of high temperaturetetrafluoroethylene or hard chrome was found to be effective for thepurposes of the present invention when applied to a core member 30consisting of an aluminum alloy. The purpose of the coating is tofacilitate the removal of the remaining portions of the core from thecylinder casting after machining the bore. Aluminum cores are currentlybeing anodized with refractory materials in order to restrict the rateof heat transfer through the core, the cast article and the outer moldsurfaces. It has been discovered. unexpectedly, that such refractoryfilm is not satisfactorily effective to preclude fusion, welding orbrazing of a cast aluminum article to an aluminum core member.

In the preferred embodiment of the present invention, a core member 30consisting of aluminum is cast and the port forming blisters, ports, andcombustion chambers are sprayed, brushed or dipped with a liquidizedpolyimide composition which may be diluted with an appropriate solventto comprise a solution comprising 50 percent to 90 percent, by volume,of polyimide. N-methylpyrrolidone has been found to be a suitablesolvent for this purpose. The liquid mm. of the polyimide solution isthen baked on the core 30 at 600 F. for 20 to 30 minutes. For bestresults, the core member 30 should be cleaned with the solvent and thendry heated before applying the polyimide composition. The cured coatingshould have a brown color and should not show any bare spots. Theuniformity of the coating thickness is not critical.

The core member 30 is then positioned within a mold as shown in FIG. 4and properly held in place by means of the cylindrical locator portion50 which projects upward from the bottom of the mold cavity 52 and,itself, provides the spherical surface 53 for forming the combustionchamber 22. Of course, the combustion chamber could alternatively beformed by a surface portion of the core member 30. The surrounding mold54 may comprise any conventional mold member because the tolerances onthe outside surfaces of a hollow article such as an engine cylinder arenot generally critical. Therefore, if the material comprising the moldmember 54 should expand at a different rate than the cast material, anyresulting minor distortion would be acceptable.

After the aluminum core 30 is properly located within the mold 54,molten aluminum is introduced through an inlet duct 56 into the articleforming surfaces of the mold member 54. The aluminum is first heated toa temperature within a range of 1200" to l225 F. and enters the cavity52 under a pressure within a range of 13,000 to 14,000 psi. The overallapparatus may then be cooled for to seconds until the aluminum hassolidified at a temperature within a range of 600 to 700 F.

After the aluminum has solidified, the mold 54, which may be of thesegmental type, is removed by any conventional means from around thearticle and the core 30 retained therein. The major portion of the coremember 30 is then machined out from the cast article. The projections38, 40 and 42 remain within the walls of the hollow cast article. Thearticle is then mechanically impacted by means of a soft hammer, or thelike, which impaction causes the remaining portions of the core memberto be loosened from within the cast article and to fall out. An accesshole may be drilled adjacent a blister forming projection to permit theknocking out of the projection by the insertion of a tool through thehole which tool may directly contact the projection and effect theremoval thereof by transmitting mechanical impactions directly thereto.

ALTERNATIVE EMBODIMENTS FIG. 5 shows a core member 30 positioned withina die member 52 which core member 30 is formed with blister formingprojections 42. The projections, in turn, are formed with radiallyextending tapered bosses 60 which extend through the cylinder 10 andinto holes 62 formed within the casting mold 52 for retaining the bosses60.

FIG. 6 shows the cast cylinder after the mold 54 has been removed andafter a major portion of the core member 30 has been machined out fromtherein. It will be appreciated, particularly with reference to FIG. 6,that the step of machining a major portion of the core from the castarticle may involve boring out the generally cylindrical portion of thecore member and leaving only the protuberances remaining distinctlyencapsulated within the wall of the cast hollow article. The blisterforming protuberances 42 have been displaced from the blisters withinthe cylinders by mechanically impacting the radial ends of the bosses 60formed thereon. Each blister forming protuberance 42 is then broken offfrom the associated boss 60 at a neck portion 63 of the boss 60. Thebosses 60 shown in FIGS. 5 and 6 are tapered to widen toward the radialends thereof. This configuration permits the boss to plug the hole thatwas formed within the cylinder 10 thereby. The use of a boss 60 to applya mechanical impaction directly to a blister forming projection 42 isespecially useful when forming off-set transfer ports such as thoseshown in FIG. 2 which ports may extend at an angle which does notcoincide with a radial line drawn from the center of the cylinder 10 toan approximate center of a blister 18. When the boss 60 is left withinthe cylinder wall to plug up the hole left thereby, it may be desirableto weld the outer portions of the boss 60 to the outer surface of thecylinder to prevent the boss from loosening and being propelled throughthe hole under the influence of any gas pressure buildup.

As shown in FIG. 7, the protuberance 42 may be formed with a boss 64having a reverse taper to that of boss 60 shown in FIG. 6.Alternatively, the protuberance 42 may be formed without a boss as shownin FIG.

8 and a hole 65 machined in the cylinder for the insertion of a punchtool 67 for removing the protuberance 42. A steel ball 69 and a sealingmaterial 71 may then be used to fill the hole 65 as shown in FIG. 9.

Also, if the aluminum core member is permitted to form an oxide layer,before casting an aluminum article, it has been found that this layermay function as an anti-adhering layer to prevent fusion between thecore and cast article. The formation of an aluminum oxide layer may beencouraged by placing a heated core in an atmosphere with an excess ofoxygen.

The removal of core protuberances is facilitated if the protuberance istapered toward the radial end thereof. It can be seen that the transferport 18 of the cylinder shown in FIG. 1 has been formed by protuberance42 of FIG. 3 which does so taper. If it should be that the protuberancesleft in the cylinder after the rough machining step are falling out tooeasily, the angle of taper may be reduced so that the cylinder retains aprotuberance until mechanically impacted. The angle of protuberancetaper is known in the art as the draft.

It can thus be seen that an apparatus and method have been hereindescribed for die casting irregular, hollow articles of manufacture suchas internal combustion engine cylinders. Since the core member used toform the hollow portion of the article may comprise the same material asthe article, the coefficient of expansion and heat transfercharacteristics of the core and of the cast article are also identicalwhich identity reduces distortion of the critical tolerances within thebaked onto the core prevents fusion, brazing or welding of the coremember with the die cast article. The machining required after themolded material solidifies in the cast article is mainly rough machiningof the interior of the cylinder which removes a major portion of thecore member. Then, the article only need be impacted to remove theremaining portions of the core as the anti-adhering coating provides forthe easy removal thereof. The removed article may then be finelymachined, plated and honed.

Through this method and apparatus, it is. no longer necessary to cast alightweight aluminum cylinder around a heavy iron liner as is thepresent practice. Since there is no iron liner within the aluminum bodyof the cylinder, distortion of the critical tolerances of the overallcylinder is reduced when the engine is run at high operatingtemperatures. Likewise, since the cylinder is not a composite ofdissimilar metals, cooling problems caused by having to conduct heatthrough such composites are avoided. Because the only machining requiredwhen practicing the present invention is the boring of a major portionof the core from the cylindrical body, the amount of expensive andtimeconsuming machining is reduced. The closer tolerances now madeavailable by the present invention provide a tighter piston fit, whichin turn prevents compression loss and blow-by which results in lowengine power and the corrosion of engine parts such as wrist pins.

While what has been shown herein are several embodiments of the presentinvention, it is, of course, understood that the method and apparatusdisclosed herein may be modified without departing from the invention.It is therefore intended to cover in the appended claims all suchmodifications as fall within the true scope and spirit of the presentinvention.

I claim:

1. A method of molding hollow articles comprising the steps of:

a. providing a mold having a cavity for forming the outer surface of thearticle;

b. providing a core member having an outer surface for forming the innersurface of the article, the outer surface of said core member includinga main body portion and at least one protuberance projecting outwardlytherefrom;

c. providing at least a portion of the article forming surface of thecore member including said at least one protuberance with ananti-adhering substance layer to prevent fusion between that portion ofthe core and the article;

d. locating the core member with in the cavity of the mold to define anarticle forming space between the outer surface of the core and theinner surface 'ofthemo e. introducing molten die casting material intosaid article forming space and in surrounding relationship with said atleast one protuberance;

. cooling the molten material until it solidifies into a cast articlewith a configuration encapsulating said at least one protuberance;

g. releasing the solidified cast article from the mold;

h. machining the main body portion of core from within the cast articleleaving only said at least one protuberance remaining, to form a hollowarticle encapsulating said at least one protuberance of the core;

i. mechanically impacting the cast article including the encapsulatedsaid at least one protuberance of the core to loosen said encapsulatedat least one protuberance free from the hollow article.

2. A method according to claim 1 wherein:

the step of providing a core member having an outer surface for formingthe inner surface of the article comprises the step of casting a hollowgenerally cylindrical metal member forming said main body portion andhaving a plurality of said protuberances projecting therefrom forforming port holes and blisters within the hollow article;

the step of providing at least a portion of the article forming surfacewith an anti-adhering substance layer comprises providing each of saidprotuberances with an anti-adhering substance layer;

the step of machining comprises forming a hollow article with each ofsaid protuberances being distinctly encapsulated by said hollow article;and wherein the step of mechanically impacting is performed so as toloosen each of said distinctly encapsulated protuberances.

3. A process according to claim 1 wherein the step of providing at leasta portion of the article forming surface with an anti-adhering substancecomprises coating said at least a portion of the core member by thesteps of:

a. applying a liquified polyimide composition to said at least a portionof the article forming surface of the core; and

b. baking the composition onto said at least a portion of the coremember.

4. A method of molding hollow articles comprising the steps of:

a. providing a mold having a cavity for forming the outer surface of thearticle;

b. providing a core member having an outer surface for forming the innersurface of the article;

c. coating at least a portion of the article forming surface of the coremember with an anti-adhering substance to prevent fusion between thatportion of the core and the article;

d. locating the core member within the mold;

e. introducing molten die casting material into the space defined by theouter surface of the core and the inner surface of the mold;

f. cooling the molten material until it solidifies;

g. releasing the solidified cast article from the mold;

h. machining a major portion of the core from within the cast article;

i. mechanically impacting the article including the remaining portion ofthe core to loosen the remaining portion of the core free from thearticle;

j. the step of coating the article-forming surface of the core membercomprising:

1. cleaning the core member with a solvent;

2. heat drying the solvent on the core;

3. applying a liquified polyimide composition to said at least a portionof the article forming surface of the core, with the polyimidecomposition being thinned to comprise a solution in the range 50 topercent by volume of the polyimide; and

4. baking the solution of polyimide and solvent on the core atapproximately 600 F. for approximately 20 to 30 minutes.

5. A method according to claim 4 wherein the solvent consists ofN-Methylpyrrolidone.

6. A method of molding hollow articles comprising the steps of:

a. providing a mold having a cavity for forming the outer surface of thearticle;

b. providing a core member having an outer surface for forming the innersurface of the article;

c. coating at least a portion of the article forming the surface of thecore member with an anti-adhering substance to prevent fusion betweenthat portion of the core and the article;

d. locating the core member within the mold;

e. introducing molten die casting material into the space defined by theouter surface of the core and the inner surface of the mold;

f. cooling the molten material until it solidifies;

releasing the solidified cast article from the mold;

h. machining a major portion of the core from within the cast article;

i. mechanically impacting the article including the remaining portion ofthe core to loosen the remaining portion of the core free from thearticle;

j. the step of introducing molten material into the space definedbetween the core and mold comprising the step of supplying moltenaluminum heated within the range of l,200- 1225 F. and subjected to apressure within the range of 13,000 14,000 psi into the space.

7. A method according to claim 6 wherein the step of cooling the moltenmaterial comprises the step of chilling the material 10-15 seconds untilthe material has a temperature within the range of 600-700 F.

8. A method of molding hollow articles comprising the steps of:

a. providing a mold having a cavity for forming the outer surface of thearticle;

b. providing a metal core member having an outer surface for forming theinner surface of the article, the outer surface of the core member beinga generally cylindrical surface having protuberances projectingtherefrom for forming port holes and blisters within the hollow article;

c. coating at least the protuberances of the article forming the surfaceof the core member with an anti-adhering substance to prevent fusionbetween those portions of the core and the article;

d. locating the core member within the mold;

e. introducing molten die casting material into the space defined by theouter surface of the core and the inner surface of the mold;

f. cooling the molten material until it solidifies;

g. releasing the solidified cast article from the mold;

h. machining a major portion of the core from within the cast article bythe step of boring out the generally cylindrical portion of the coremember and leaving only the protuberances remaining within the wall ofthe cast article; and

i. mechanically impacting the article including the remaining portion ofthe core to loosen the remaining portion of the core free from thearticle.

9. A method according to claim 2 wherein the core member comprises ametal taken from the group consisting of aluminum and magnesium.

10. An article of manufacture made in accordance with the steps of themethod recited in claim 1.

11. A method for manufacturing hollow articles comprising the steps:

a. casting an article within a mold having a generally cylindrical coremember located therein, the outer surface of the generally cylindricalcore member including a main body portion and at least one protuberanceprojecting outwardly therefrom;

b. providing said at least one protuberance with an anti-adheringsubstance to prevent fusion to the article;

c. removing the article and core from the mold;

d. removing the entire main body portion of the generally cylindricalcore from the article leaving only said at least one protuberanceremaining within the wall of the cast article; and

e. mechanically impacting the article to loosen and knock out said atleast one protuberance from within the article.

12. The method according to claim 11 wherein the core is cooled beforecasting the article.

13. A method for manufacturing hollow articles comprising the steps of:

a. casting an article within a mold having a core member locatedtherein;

b. removing the article and core from the mold;

c. removing a major portion of the core from the article; and

d. mechanically impacting the article to loosen and knock out theremaining portion of the core from within the article;

e. the method including the step of forming an oxide coating on theoutside surfaces of the core.

14. The method according to claim 1 wherein the step of providing a coremember comprises providing a core member with the main body portion ofits outer article forming surface being generally cylindrical and havinga plurality of said protuberances projecting outwardly therefrom forforming port holes and blisters within the hollow article, and whereineach of said protuberances are provided with an anti-adhering layer andare left remaining after the machining step for loosening by theimpacting step.

1. A method of molding hollow articles comprising the steps of: a.providing a mold having a cavity for forming the outer surface of thearticle; b. providing a core member having an outer surface for formingthe inner surface of the article, the outer surface of said core memberincluding a main body portion and at least one protuberance projectingoutwardly therefrom; c. providing at least a portion of the articleforming surface of the core member including said at least oneprotuberance with an anti-adhering substance layer to prevent fusionbetween that portion of the core and the article; d. locating the coremember with in the cavity of the mold to define an article within spacebetween the outer surface of the core and the inner surface of the mold;e. introducing molten die casting material into said article formingspace and in surrounding relationship with said at least oneprotuberance; f. cooling the molten material until it solidifies into acast article with a configuration encapsulating said at least oneprotuberance; g. releasing the solidified cast article from the mold; h.machining the main body portion of core from within the cast articleleaving only said at least one protuberance remaining, to form a hollowarticle encapsulating said at least one protuberance of the core; i.mechanically impacting the cast article including the encapsulated saidat least one protuberance of the core to loosen said encapsulated atleast one protuberance free from the hollow article.
 2. heat drying thesolvent on the core;
 2. A method according to claim 1 wherein: the stepof providing a core member having an outer surface for forming the innersurface of the article comprises the step of casting a hollow generallycylindrical metal member forming said main body portion and having aplurality of said protuberances projecting therefrom for forming portholes and blisters within the hollow article; the step of providing atleast a portion of the article forming surface with an anti-adheringsubstance layer comprises providing each of said protuberances with ananti-adhering substance layer; the step of machining comprises forming ahollow article with each of said protuberances being distinctlyencapsulated by said hollow article; and wherein the step ofmechanically impacting is performed so as to loosen each of saiddistinctly encapsulated protuberances.
 3. applying a liquified polyimidecomposition to said at least a portion of the article forming surface ofthe core, with the polyimide composition being thinned to comprise asolution in the range 50 to 90 percent by volume of the polyimide; and3. A process according to claim 1 wherein the step of providing at leasta portion of the article forming surface with an anti-adhering substancecomprises coating said at least a portion of the core member by thesteps of: a. applying a liquified polyimide composition to said at leasta portion of the article forming surface of the core; and b. baking thecomposition onto said at least a portion of the core member.
 4. A methodof molding hollow articles comprising the steps of: a. providing a moldhaving a cavity for forming the outer surface of the article; b.providing a core member having an outer surface for forming the innersurface of the article; c. coating at least a portion of the articleforming surface of the core member with an anti-adhering substance toprevent fusion between that portion of the core and the article; d.locating the core member within the mold; e. introducing molten diecasting material into the space defined by the outer surface of the coreand the inner surface of the mold; f. cooling the molten material untilit solidifies; g. releasing the solidified cast article from the mold;h. machining a major portion of the core from within the cast article;i. mechanically impacting the article including the remaining portion ofthe core to loosen the remaining portion of the core free from thearticle; j. the step of coating the article-forming surface of the coremember comprising:
 4. baking the solution of polyimide and solvent onthe core at approximately 600* F. for approximately 20 to 30 minutes. 5.A method according to claim 4 wherein the solvent consists ofN-Methylpyrrolidone.
 6. A method of molding hollow articles comprisingthe steps of: a. providing a mold having a cavity for forming the outersurface of the article; b. providing a core member having an outersurface for forming the inner surface of the article; c. coating atleast a portion of the article forming the surface of the core memberwith an anti-adhering substance to prevent fusion between that portionof the core and the article; d. locating the core member within themold; e. introducing molten die casting material into the space definedby the outer surface of the core and the inner surface of the mold; f.cooling the molten material until it solidifies; g. releasing thesolidified cast article from the mold; h. machining a major portion ofthe core from within the cast article; i. mechanically impacting thearticle including the remaining portion of the core to loosen theremaining portion of the core free from the article; j. the step ofintroducing molten material into the space defined between the core andmold comprising the step of supplying molten aluminum heated within therange of 1,200* -1225* F. and subjected to a pressure within the rangeof 13,000 - 14,000 psi into the space.
 7. A method according to claim 6wherein the step of cooling the molten material comprises the step ofchilling the material 10-15 seconds until the material has a temperaturewithin the range of 600*-700* F.
 8. A method of molding hollow articlescomprising the steps of: a. providing a mold having a cavity for formingthe outer surface of the article; b. providing a metal core memberhaving an outer surface for forming the inner surface of the article,the outer surface of the core member being a generally cylindricalsurface having protuberances projecting therefrom for forming port holesand blisters within the hollow article; c. coating at least theprotuberances of the article forming the surface of the core member withan anti-adhering substance to prevent fusion between those portions ofthe core and the article; d. locating the core member within the mold;e. introducing molten die casting material into the space defined by theouter surface of the core and the inner surface of the mold; f. coolingthe molten material until it solidifies; g. releasing the solidifiedcast article from the mold; h. machining a major portion of the corefrom within the cast article by the step of boring out the generallycylindrical portion of the core member and leaving only theprotuberances remaining within the wall of the cast article; and i.mechanically impacting the article including the remaining portion ofthe core to loosen the remaining portion of the core free from thearticle.
 9. A method according to claim 2 wherein the core membercomprises a metal taken from the group consisting of aluminum andmagnesium.
 10. An article of manufacture made in accordance with thesteps of the method recited in claim
 1. 11. A method for manufacturinghollow articles comprising the steps: a. casting an article within amold having a generally cylindrical core member located therein, theouter surface of the generally cylindrical core member including a mainbody portion and at least one protuberance projecting outwardlytherefrom; b. providing said at least one protuberance with ananti-adhering substance to prevent fusion to the article; c. removingthe article and core from the mold; d. removing the entire main bodyportion of the generally cylindrical core from the article leaving onlysaid at least one protuberance remaining within the wall of the castarticle; and e. mechanically impacting the article to loosen and knockout said at least one protuberance from within the article.
 12. Themethod according to claim 11 wherein the core is cooled before castingthe article.
 13. A method for manufacturing hollow articles comprisingthe steps of: a. casting an article within a mold having a core memberlocated therein; b. removing the article and core from the mold; c.removing a major portion of the core from the article; and d.mechanically impacting the article to loosen and knock out the remainingportion of the core from within the article; e. the method including thestep of forming an oxide coating on the outside surfaces of the core.14. The method according to claim 1 wherein the step of providing a coremember comprises providing a core member with the main body portion ofits outer article forming surface being generally cylindrical and havinga plurality of said protuberances projecting outwardly therefrom forforming port holes and blisters within the hollow article, and whereineach of said protuberances are provided with an anti-adhering layer andare left remaining after the machining step for loosening by theimpacting step.